LibMedia: Make Track::type() const

Author: https://github.com/Zaggy1024
Commit: 31b72c4799
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/6410
Reviewed-by: https://github.com/R-Goc
Reviewed-by: https://github.com/gmta ✅

Libraries/LibMedia/Track.h

@@ -42,7 +42,7 @@ public:
         }
     }
 
-    TrackType type() { return m_type; }
+    TrackType type() const { return m_type; }
     size_t identifier() const { return m_identifier; }
 
     void set_video_data(VideoData data)